Rolling mill piercing point, plug and guide, and method of making same



H. F TIELKE May 26, 1931.

ROLLING MILL PIERCING POINT, PLUG, AND GUIDE, AND METHOD OF MAKING SAME Filed Aug HOMERF T E K'E dam/M 5 Patented May 26, 1931 UNITED STATES HOMER F. TIELKE, OF CLEVELAND, OHIO PATENT 'oFncE ROLLING MILL PIERCING POINT, PLUG AND GUIDE, HETHQD OIEfiAKING SAME Application filed August as, 192a. Serial No. 387,910.

This invention relates to steel alloys and to methods of heat treating the same. It also relates to articles for use in rolling mills such as piercing points, plugs and guides and other parts which are subjected to high compressive and frictional loads.

Heretofore such enumerated articles have usually been made of steel alloys containing chromium, and nickel but have not been satisfactory for the severe uses and service conditions to which they are subjected, this being particularly true in piercing points. Such material has been characterized by brittleness which often resulted in breakage of the arti- 16 cles before they had been worn out, and in-- repeatedly and for many times the amount of service given by the prior art articles.

, According to the present invention a high carbon steel alloy is employed containing between about .7 5% and about 1.5% of carbon, between about 16% and about 19% of chromium and between about 2% and about 4% of cobalt. Nickel may also be resent in the alloy in amounts of between about .4% and about 2% if desired. Tungsten may be present in the alloy in amounts up to about 2% if desired but satisfactory results have been obtained without the presence of tungsten. A preferred composition is a steel alloy containing about .80% of carbon, about 17% of chromium, about of cobalt and about .60% of nickel- In adapting alloys of this invention to use guides and the like, the alloy is preferab y cast in asand mold as nearly to sue as pos sible and the castin is then ground to remove.

in such articles as piercing points, plu s,'

treated to bring about micro-structure which is characterized by consisting of homogeneous dendritic material of substantially uniform hardness. This may be accomplished by heat treatingthe casting as follows:

The casting is heated up to about 2250 F. for a period of time suificient to insure that the interior of the casting has been brought to substantially such temperature. With piercing ,points a period of about five minutes at a temperature of 2250? F. is suflicient for this purpose but it will be understood that this length of' time will depend somewhat on the size of the article being heated and the number of articles being heated at the same about six hours having been found to be satisfactory for piercing points, rolling mill plugs and the like.

Articles composed of the foregoing alloys when treated according to the foregoing methods possess a micro-structure which is characteristically dendritic and martensitic, resembles tool steel as to grain size, and is homogeneous and of substantially uniform hardness throughout. It is characterized also by the absence of grains surrounded by ain boundary material of a markedly different hardness which is characteristic of the material in the as-cast condition.

I believe that when alloys of the foregoing composition are cast the higher meltin point constituents are surrounded by grain fioundary material of a (lifi'erent hardness and that the step of heating to about 2250 F. or well above the upper critical range of thealloy results in bringing about a dissolving action which removes much of, if not all, the grain boundary material. The cooling in air is at such a rate that the latter material does not precipitate out of the solid solution and the" i re-heating step which is carried out above the, upper critical range of the alloy results,

in part at least, in a refining of the structure of the casting which structure is retained and prevented from grain growth by the oil quenching step. The final heating is carried out at such a temperature that the previously refined grains are prevented from material growth and any casting strains which may remain in the casting are removed and the structure is made more nearly uniform in treated casting having the above mentioned preferred com position;

Figure 2 is a view of the same material at the same magnification but taken afterthe material of Figure 1 had been heat treated according to the foregoing method.

Having thus described my invention so.

i that those skilled in the art may be enabled to practice the same what I desire to secure by Letters Patent is defined in what is claimed, it being understood that variations and changes in the composition of the alloy or in the steps of the method may be made without departing from the scope of my invention as claimed.

What is claimed is:

1. A steel alloy containing between about 17, and about 18% of chromium, about 3% of cobalt and between about .4% and 1.5% of nickel, and having a structure charactcristic of such an alloy which has been heatedin cast form to about 2250 F. for about five minutes, cooled slowly, reheated to between about 140() F. and about -1800 F., quenched and reheated at about 1200 F. for several hours. i

2. A heat treated steel. alloy article hav. ing a microstructurc characteristic of high carbon steel containing between about 16% and about 19% of chromium and about 2% and about 4% of cobalt, which has been heated to about 2250 F. for about five minutes, cooled slowly, reheated to between about 1400 F1 and about 1800 F. and quenched and then reheated to about 1200 F. for about six hours. i

3. A heat treated steel alloy article having a microstructure characteristic of high carbon steel containing between about .75% and about 1.5% of carbon, between about 16% and about 19% chromium and between about 2% and about 4% of cobalt, which has been heated to about 2250 F. for about five minutes, cooled in air, reheated to about 1800 -to about 1200 F. for about six hours.

4. A heat treated steel alloy article having a microstructure characteristic of high carbon steel containing between about .75% and about 1.5% of carbon, between about 16% and about 19% of chromium and between about 2% and about 4% of cobalt, and between about .4% and about 2% of nickel, which has been heated to about 2250 F. for about five minutes, cooled in air, reheated to about 1800 F. and quenched and then reheated to about 1200 F. for about six hours.

5. The method of .heat treating a steel'al- 10y casting containing between about .75%

and about 1.5% of carbon, between about length of time to bring into solid solution a major part of the 'rain boundary material, cooling the casting m a manner to retain such dissolved grain boundary material in solid solution, reheating the casting to a temperature above the upper critical ranged sufiiciently long to bring about a refining of the grain structure, quenching the refined structure, and then heating the casting at such a temperature and for a sufiiciently prolonged time to produce a dendritic homogeneous structure of substantially lllllfOlll'l hardness throughout.

.7. A heat treated rolling mill piercing point, plug or guide composed of a steel alloy containing"between about .75% and about 1.5% of carbon,-bet\ veen about 16% and about 18% of chromium and between about 2% and about 4% ofcobalt and having a microstructure characterized by bein dendritic, homogeneous and of substanti ly uniform hardnessthroughout. and having a micro- 

